Method and system for split voltage domain receiver circuits

ABSTRACT

Methods and systems for split voltage domain receiver circuits are disclosed and may comprise amplifying received electrical signals in a plurality of partial voltage domains, and combining the amplified received signals, utilizing a stacked cascode amplifier for each partial voltage domain, into a single differential signal in a single voltage domain. The stacked cascode amplifiers may comprise a feedback loop having a comparator which controls a current source in each domain. The signals may be received from a photodiode, which may be integrated in the integrated circuit. The amplified signals may be combined via stacked common source or common emitter amplifiers. The received signals via may be amplified by stacked inverters. The amplified received signals may be AC or DC coupled prior to the combining. The received electrical signals may be amplified and combined via cascode amplifiers. The voltage domains may be stacked and may be controlled by feedback loops.

CROSS-REFERENCE TO RELATED APPLICATIONS/INCORPORATION BY REFERENCE

This application makes reference to and claims priority to U.S.Provisional Application Ser. No. 60/997,282 filed on Oct. 2, 2007, whichis hereby incorporated herein by reference in its entirety.

This application also makes reference to:

U.S. patent application Ser. No. 12/208,650 filed on even date herewith.

Each of the above stated applications is hereby incorporated herein byreference in its entirety.

FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[Not Applicable]

MICROFICHE/COPYRIGHT REFERENCE

[Not Applicable]

FIELD OF THE INVENTION

Certain embodiments of the invention relate to integrated circuit powercontrol. More specifically, certain embodiments of the invention relateto a method and system for split voltage domain receiver circuits.

BACKGROUND OF THE INVENTION

Electronic circuits typically require a bias voltage for properoperation. The voltage level required by a circuit depends on theapplication. A circuit for transmitting electromagnetic radiation mayrequire a higher voltage than a circuit used for processing data. Theoptimum voltage may be determined by the bias voltage requirements ofthe transistors, or other active devices, within the circuit.

A bipolar transistor circuit may require a higher voltage in amplifierapplications to avoid saturation of the amplifier, as opposed toswitching operations, for example. CMOS circuits may require a lowervoltage to drive the MOSFETs in the circuit.

Furthermore, as device sizes continue to shrink for higher speed andlower power consumption, a high voltage may degrade performance andcause excessive leakage. With thinner gate oxides, gate leakage currentmay become significant using historical bias voltages, thus driving gatevoltages lower. However, if a transmitter/receiver may be integrated inthe same device, a higher bias voltage may also be required. Biasvoltages are typically DC voltage, and may be supplied by a battery.However, there may be noise in the bias voltage, which may be mitigatedby capacitive filters. The variable output voltage of batteries myaffect operation of battery powered devices. Devices generally must becapable of operating over a large range of voltage due to the variableoutput voltage capability of batteries.

Further limitations and disadvantages of conventional and traditionalapproaches will become apparent to one of skill in the art, throughcomparison of such systems with the present invention as set forth inthe remainder of the present application with reference to the drawings.

BRIEF SUMMARY OF THE INVENTION

A system and/or method for split voltage domain receiver circuits,substantially as shown in and/or described in connection with at leastone of the figures, as set forth more completely in the claims.

Various advantages, aspects and novel features of the present invention,as well as details of an illustrated embodiment thereof, will be morefully understood from the following description and drawings.

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS

FIG. 1A is a block diagram of a photonically enabled CMOS chip, inaccordance with an embodiment of the invention.

FIG. 1B is a diagram illustrating an exemplary CMOS chip, in accordancewith an embodiment of the invention.

FIG. 1C is a diagram illustrating an exemplary CMOS chip coupled to anoptical fiber cable, in accordance with an embodiment of the invention.

FIG. 1D is a block diagram of an exemplary n-type field effecttransistor circuit, in accordance with an embodiment of the invention.

FIG. 1E is a block diagram of an exemplary p-type field effecttransistor circuit, in accordance with an embodiment of the invention.

FIG. 2 is a block diagram of an exemplary two-domain receiver circuit,in accordance with an embodiment of the invention.

FIG. 3 is a schematic of an exemplary transimpedance amplifier domaincombiner, in accordance with an embodiment of the invention.

FIG. 4 is a flow chart illustrating exemplary steps in the operation ofa split domain transimpedance amplifier with domain combiner, inaccordance with an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Certain aspects of the invention may be found in a method and system forsplit voltage domain receiver circuits. Exemplary aspects of theinvention may comprise amplifying complementary received signals in aplurality of partial voltage domains. The signals may be combined into asingle differential signal in a single voltage domain. Each of thepartial voltage domains may be offset by a DC voltage from the otherpartial voltage domains. The sum of the partial domains may be equal toa supply voltage of the integrated circuit. The complementary signalsmay be received from a photodiode. The amplified received signals may beamplified via stacked common source amplifiers, common emitteramplifiers, or stacked inverters. The amplified received signals may beDC coupled prior to combining. The complementary received signals may beamplified and combined via cascode amplifiers. The voltage domains maybe stacked, and may be controlled via feedback loops. The photodetectormay be integrated in the integrated circuit.

FIG. 1A is a block diagram of a photonically enabled CMOS chip, inaccordance with an embodiment of the invention. Referring to FIG. 1A,there is shown optoelectronic devices on a CMOS chip 130 comprising highspeed optical modulators 105A-105D, high-speed photodiodes 111A-111D,monitor photodiodes 113A-113H, and optical devices comprising taps103A-103K, optical terminations 115A-115D, and grating couplers117A-117H. There is also shown electrical device and circuits comprisingtransimpedance and limiting amplifiers (TIA/LAs) 107A-107D, analog anddigital control circuits 109, and control sections 112A-112D. Opticalsignals are communicated between optical and optoelectronic devices viaoptical waveguides fabricated in the CMOS chip 130.

The high speed optical modulators 105A-105D comprise Mach-Zehnder orring modulators, for example, and enable the modulation of the CW laserinput signal. The high speed optical modulators 105A-105D are controlledby the control sections 112A-112D, and the outputs of the modulators areoptically coupled via waveguides to the grating couplers 117E-117H. Thetaps 103D-103K comprise four-port optical couplers, for example, and areutilized to sample the optical signals generated by the high speedoptical modulators 105A-105D, with the sampled signals being measured bythe monitor photodiodes 113A-113H. The unused branches of the taps103D-103K are terminated by optical terminations 115A-115D to avoid backreflections of unwanted signals.

The grating couplers 117A-117H comprise optical gratings that enablecoupling of light into and out of the CMOS chip 130. The gratingcouplers 117A-117D are utilized to couple light received from opticalfibers into the CMOS chip 130, and the grating couplers 117E-117H areutilized to couple light from the CMOS chip 130 into optical fibers. Theoptical fibers may be epoxied, for example, to the CMOS chip, and may bealigned at an angle from normal to the surface of the CMOS chip 130 tooptimize coupling efficiency.

The high-speed photodiodes 111A-111D convert optical signals receivedfrom the grating couplers 117A-117D into electrical signals that arecommunicated to the TIA/LAs 107A-107D for processing. The electricalsignals generated by the high-speed photodiodes 111A-111D may be sensedin differential mode and amplified in a plurality of voltage domains.The sum of the individual voltage domains may sum up to the supplyvoltage. In this manner, the voltage swing across each stage of thereceiver circuitry, such as stacked inverters, may be halved, whilestill providing the same photogenerated current, thus doubling the gain,improving the signal to noise ratio and the efficiency. The signals maythen be combined into a single voltage domain via stacked common sourceamplifiers, for example. The analog and digital control circuits 109 maycontrol gain levels or other parameters in the operation of the TIA/LAs107A-107D. The TIA/LAs 107A-107D then communicate electrical signals offthe CMOS chip 130.

The control sections 112A-112D comprise electronic circuitry that enablemodulation of the CW laser signal received from the splitters 103A-103C.The high speed optical modulators 105A-105D require high-speedelectrical signals to modulate the refractive index in respectivebranches of a Mach-Zehnder interferometer (MZI), for example. Thevoltage swing required for driving the MZI is a significant power drainin the CMOS chip 130. Thus, if the electrical signal for driving themodulator may be split into domains with each domain traversing a lowervoltage swing, power efficiency is increased. Photogenerated signals maybe sensed at both terminals of a photodiode, increasing the powerefficiency, and then amplified in separate voltage domains.

FIG. 1B is a diagram illustrating an exemplary CMOS chip, in accordancewith an embodiment of the invention. Referring to FIG. 1B, there isshown the CMOS chip 130 comprising electronic devices/circuits 131,optical and optoelectronic devices 133, a light source interface 135,CMOS chip surface 137, an optical fiber interface 139, and CMOS guardring 141.

The light source interface 135 and the optical fiber interface 139comprise grating couplers that enable coupling of light signals via theCMOS chip surface 137, as opposed to the edges of the chip as withconventional edge-emitting devices. Coupling light signals via the CMOSchip surface 137 enables the use of the CMOS guard ring 141 whichprotects the chip mechanically and prevents the entry of contaminantsvia the chip edge.

The electronic devices/circuits 131 comprise circuitry such as theTIA/LAs 107A-107D and the analog and digital control circuits 109described with respect to FIG. 1A, for example. The optical andoptoelectronic devices 133 comprise devices such as the taps 103A-103K,optical terminations 115A-115D, grating couplers 117A-117H, high speedoptical modulators 105A-105D, high-speed photodiodes 111A-111D, andmonitor photodiodes 113A-113H.

FIG. 1C is a diagram illustrating an exemplary CMOS chip coupled to anoptical fiber cable, in accordance with an embodiment of the invention.Referring to FIG. 1C, there is shown the CMOS chip 130 comprising theelectronic devices/circuits 131, the optical and optoelectronic devices133, the light source interface 135, the CMOS chip surface 137, and theCMOS guard ring 141. There is also shown a fiber to chip coupler 143, anoptical fiber cable 145, and a light source module 147.

The CMOS chip 130 comprising the electronic devices/circuits 131, theoptical and optoelectronic devices 133, the light source interface 135,the CMOS chip surface 137, and the CMOS guard ring 141 may be asdescribed with respect to FIG. 1B.

In an embodiment of the invention, the optical fiber cable may beaffixed, via epoxy for example, to the CMOS chip surface 137. The fiberchip coupler 143 enables the physical coupling of the optical fibercable 145 to the CMOS chip 130.

The light source module 147 may be affixed, via epoxy or solder, forexample, to the CMOS chip surface 137. In this manner a high power lightsource may be integrated with optoelectronic and electronicfunctionalities of one or more high-speed optoelectronic transceivers ona single CMOS chip.

The power requirements of optoelectronic transceivers is an importantparameter. Minimizing voltage swings is one option for reducing powerusage, and operating photodiodes in differential mode enable reducedpower consumption with improved signal to noise ratio. Photogeneratedsignals may be sensed at both terminals of a photodiode and amplified inseparate voltage domains. Following the amplification of thephotogenerated signals, they may be combined into a single voltagedomain prior to subsequent processing, such as digital processing, forexample.

FIG. 1D is a block diagram of an exemplary n-type field effecttransistor circuit, in accordance with an embodiment of the invention.Referring to FIG. 1D, there is shown a source follower circuit 55comprising an n-channel field effect transistor (NFET) 50, a resistor33, a high rail 20, and a low rail 10. There is also shown a circuitinput 100 and a circuit output 200.

The source follower circuit 55 has two power rails, comprising the highrail 20 biased at a voltage V_(f), or full voltage, and the low rail 10,marked with the customary symbol of “ground”. The circuit has an input100 on the gate of the NFET 50, while the circuit output 200 is on theNFET source side, or simply source. The NFET 50 drain side, or drain, isconnected to the high rail 20. The resistor 33 is coupled between thesource terminal of the NFET 50 and the low rail 10, completing anelectrical path between the high 20 and low 10 rails.

In operation, an input signal is applied to the input 100. The sourcefollower circuit 55 may be utilized to lower the impedance level in thesignal path, drive resistive loads, or to provide DC level shifting,since the gate-source DC voltage drop may be controllable by the biascurrent. The gain of the source follower circuit 55 may be near unity,resulting in an AC output signal at the circuit output 200, but with aconfigurable DC output level.

FIG. 1E is a block diagram of an exemplary p-type field effecttransistor circuit, in accordance with an embodiment of the invention.Referring to FIG. 1 E, there is shown a source follower circuit 65comprising a p-channel field effect transistor (PFET) 60, a currentsource 33′, a high rail 20, and a low rail 10. There is also shown acircuit input 100′ and a circuit output 200′.

The PFET source follower has two power rails, comprising a high rail 20at a voltage V_(f), or full voltage, and a low rail 10, marked with the“ground” symbol. The circuit has an input 100′ on the PFET 60 gate,while the circuit output 200′ is on the PFET 60 source side, or simplysource. The PFET 60 drain side, or drain, is connected to the low rail10. The current source 33′ is coupled to the high rail 20 and the PFET60 source, completing an electrical path between the high 20 and low 10rails.

In operation, an input signal is applied to the input 100′. The sourcefollower circuit 65 may be utilized to lower the impedance level in thesignal path, drive resistive loads, or to provide DC level shifting,since the gate-source DC voltage drop may be controllable by the biascurrent. The gain of the source follower circuit 65 may be near unity,resulting in a similar AC output signal at the circuit output 200′, butwith a configurable DC output level.

FIG. 2 is a block diagram of an exemplary two-domain receiver circuit,in accordance with an embodiment of the invention. Referring to FIG. 2,there is shown a stacked domain transimpedance amplifier (TIA) 250comprising compensation resistors R1 and R2, feedback resistors R3 andR4, PMOS transistors M1 and M3, and NMOS transistors M2 and M4. There isalso shown a photodiode PD1, bias voltage V_(dd), and an output signaldefined by V_(out)+ and V_(out)−. Although the circuit in FIG. 2 shows aground connection at the source terminal of NMOS transistor M4 and oneterminal of the compensation resistor R2, the invention is not solimited. Accordingly, a bias voltage may be applied instead of ground toincrease or decrease the voltage swing as desired.

The interconnection of the transistor pairs M1/M2 and M3/M4 comprise astacked inverter pair and enables the generation of a differentialsignal at V_(out)+ and V_(out)− from the electrical signal generated bythe photodiode PD1 when subjected to an optical signal. In an exemplaryembodiment, the coupling point, V_(B), at the source terminal of theNMOS transistor M2 and the PMOS transistor M3 is configured to be equalto V_(dd)/2, thus generating two voltage domains of equal magnitude. Thetuning of this voltage may be enabled by the compensation resistors R1and R2, with variations in the transistor devices, for example, as asource of imbalance. The feedback resistors R3 and R4 may flatten thegain curve of the amplifiers defined by M1/M2 and M3/M4, respectively,and result in increased bandwidth. In another embodiment of theinvention, the stacked inverters may be cascoded for increased outputimpedance and stage gain.

In operation, an optical signal is applied to the photodiode PD1. Theelectrical signal generated by the photodiode PD1 may be amplified bythe stacked inverters M1/M2 and M3/M4. By biasing V_(B) at V_(dd)/2, andapplying the photodiode PD1 signal to each of the inverters defined byM1/M2 and M3/M4, the photodiode PD1 is thus monitored in a complementarymode. In this manner, the gain may be double that of a single inverterbut at the same photodiode current, thus increasing the signal to noiseratio and increasing power efficiency. This configuration has anadvantage over conventional designs for generating differential signals,in that DC coupling is possible with the present invention, eliminatingthe low frequency corner issue from AC coupling capacitors at theoutputs of a conventional amplifier.

FIG. 3 is a schematic of an exemplary transimpedance amplifier domaincombiner, in accordance with an embodiment of the invention. Referringto FIG. 3, there is shown a TIA combiner 300 comprising PMOS transistorsM5, M6, M9, and M10, NMOS transistors M7, M8, M11, and M12, currentsources 301A and 301B, comparators 303A and 303B, and compensationresistors R5 and R6. There is also shown input terminals V_(in)+ andV_(in)− at the gate terminals of transistors M5 and M10, respectively,and output terminals V_(out)+ and V_(out)−.

The gate terminal of transistor M8 may be coupled to V_(dd), the gateterminals of transistors M6 and M11 may be coupled to V_(dd)/2, and thegate terminal of transistor M9 may be coupled to ground. In this manner,the bias conditions for the stacked cascodes in a common sourceconfiguration may define two voltage domains centered around V_(dd)/2,and the signals communicated to the two inputs at V_(in)+ and V_(in)−may see the same loading and thus the same latency, but with a DCoffset. In instances where the loading is not symmetric, jitter wouldresult.

In operation, complementary input signals in separate voltage domains,as described with respect to FIG. 2, may be coupled to the inputterminals V_(in)+ and V_(in)−. The input signals may then be amplifiedand combined into a common domain by the separate voltage domaincascodes comprising the transistors M5/M6/M7/M8 and M9/M10/M11/M12,respectively, resulting in a differential signal at the V_(out)+ andV_(out)− outputs. The interconnection of the common source amplifiersresults in a combining of the separate domains. An increase in themagnitude of the received photogenerated differential signal, i.e. thevoltage difference between V_(in)+ and V_(in)− is increasing, results inan increased potential at V_(out)+ due to transistor M8 being biased inan ON state and transistor M7 conducting more current with increasinggate voltage, pulling V_(out)+ toward V_(dd). Similarly, with transistorM9 biased ON with its gate at ground and transistor M10 conducting morecurrent with reduced gate voltage, V_(out)− is thus pulled towardsground. Conversely, a decrease in the magnitude of the receivedphotogenerated signal results in an increase at V_(out)− with transistorM5 more conductive due to the reduced gate voltage, and a decrease atV_(out)+ with transistor M12 more conductive due to the increased gatevoltage at V_(in)−.

The compensation resistors R5 and R6 may enable sensing of the DCvoltage at the V_(out)+ and V_(out)− outputs, respectively, which may becompared to a voltage reference by the comparators 303A and 303B, whichmay then adjust the DC level of the differential signal to V_(dd)/2 byadjusting the current in the current sources 301A and 301B. The currentsources 301A and 301B may comprise push-pull capability to source orsink current, thereby controlling the DC level to the midpoint,V_(dd)/2.

FIG. 4 is a flow chart illustrating exemplary steps in the operation ofa split domain transimpedance amplifier with domain combiner, inaccordance with an embodiment of the invention. In step 403, after startstep 401, a photogenerated signal may be sensed at both the anode andcathode of a photodiode. In step 405, the two electrical signals may beamplified by different voltage domain circuitry to reduce the voltageswing in each domain. In step 407, the signal may be amplified and/orinverted and combined into a single voltage domain. In step 409, aV_(dd)/2 differential signal may be output, followed by end step 411.

In an embodiment of the invention, a method and system are disclosed foramplifying complementary received signals in a plurality of partialvoltage domains. The signals may be combined into a single differentialsignal in a single voltage domain. Each of the partial voltage domainsmay be offset by a DC voltage from the other partial voltage domains.The sum of the partial domains may be equal to a supply voltage of theintegrated circuit 130. The complementary signals may be received from aphotodiode PD1. The amplified received signals may be amplified viastacked common source amplifiers, common emitter amplifiers, or stackedinverters M1/M2/M3/M4. The amplified received signals may be DC coupledprior to combining. The complementary received signals may be amplifiedand combined via cascode amplifiers M5/M6/M7/M8 and M9/M10/M11/M12. Thevoltage domains may be stacked, and may be controlled via feedbackloops. The photodetector PD1 may be integrated in the integrated circuit130.

While the invention has been described with reference to certainembodiments, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted withoutdeparting from the scope of the present invention. In addition, manymodifications may be made to adapt a particular situation or material tothe teachings of the present invention without departing from its scope.Therefore, it is intended that the present invention not be limited tothe particular embodiments disclosed, but that the present inventionwill include all embodiments falling within the scope of the appendedclaims.

What is claimed is:
 1. A method for processing signals, the methodcomprising: in an integrated circuit: amplifying received electricalsignals in a plurality of partial voltage domains; and combining saidamplified received signals, utilizing a stacked cascode amplifier foreach partial voltage domain, into a single differential signal in asingle voltage domain, said stacked cascode amplifiers comprising afeedback loop having a comparator which controls a current source ineach domain.
 2. The method according to claim 1, comprising receivingsaid electrical signals from a photodiode monitored in a complementarymode.
 3. The method according to claim 2, wherein said photodiode isintegrated in said integrated circuit.
 4. The method according to claim1, comprising combining said amplified received signals via stackedcommon source amplifiers.
 5. The method according to claim 1, comprisingcombining said amplified received signals via stacked common emitteramplifiers.
 6. The method according to claim 1, comprising amplifyingsaid received signals via stacked inverters.
 7. The method according toclaim 1, comprising DC coupling said amplified received signals prior tosaid combining.
 8. The method according to claim 1, comprising ACcoupling said amplified received signals prior to said combining.
 9. Themethod according to claim 1, comprising amplifying and combining saidreceived signals via cascode amplifiers.
 10. The method according toclaim 1, wherein said voltage domains are stacked.
 11. The methodaccording to claim 10, comprising controlling said stacked voltagedomains via feedback loops.
 12. A system for processing signals, thesystem comprising: in an integrated circuit, one or more circuitsoperable to amplify received electrical signals in a plurality ofpartial voltage domains; and said one or more circuits being operable tocombine said amplified received signals into a single differentialsignal, utilizing a stacked cascode amplifier for each partial voltagedomain, in a single voltage domain, said stacked cascode amplifierscomprising a feedback loop having a comparator which controls a currentsource in each domain.
 13. The system according to claim 12, whereinsaid one or more circuits are operable to receive said electricalsignals from a photodiode monitored in a complementary mode.
 14. Thesystem according to claim 13, wherein said photodiode is integrated insaid integrated circuit.
 15. The system according to claim 12, whereinsaid one or more circuits are operable to combine said amplifiedreceived signals via stacked common source amplifiers.
 16. The systemaccording to claim 12, wherein said one or more circuits combine saidamplified received signals via stacked common emitter amplifiers. 17.The system according to claim 12, wherein said one or more circuitsamplify said received signals via stacked inverters.
 18. The systemaccording to claim 12, wherein said one or more circuits are operable toDC couple said amplified received signals prior to said combining. 19.The system according to claim 12, wherein said one or more circuits areoperable to AC couple said amplified received signals prior to saidcombining.
 20. The system according to claim 12, wherein said one ormore circuits are operable to amplify and combine said received signalsvia cascode amplifiers.
 21. The system according to claim 12, whereinsaid voltage domains are stacked.
 22. The system according to claim 12wherein said one or more circuits are operable to control said stackedvoltage domains via feedback loops.